Repeated treatment with a low dose of reserpine as a progressive model of Parkinson's disease

Cerebrolysin potentiates the antidepressant effect of lithium in a rat model of depression

RATIONALE

Depression is the most prevalent psychiatric disorder worldwide. Although numerous antidepressant treatments are available, there is a serious clinical concern due to their severe side effects and the fact that some depressed patients are resistant to them. Lithium is the drug of choice for bipolar depression and has been used as adjunct therapy with other groups of antidepressants.

OBJECTIVES

The present study aims to investigate the effect of lithium augmentation with cerebrolysin on the neurochemical, behavioral and histopathological alterations induced in the reserpine model of depression.

METHODS

The animals were divided into control and reserpine-induced model of depression. The model animals were further divided into rat model of depression, rat model treated with lithium, rat model treated with cerebrolysin and rat model treated with a combination of lithium and cerebrolysin.

RESULTS

Treatment with lithium, cerebrolysin, or their combination alleviated most of the changes in behavior, oxidative stress parameters, acetylcholinesterase and monoamines in the cortex and hippocampus of the reserpine-induced model of depression. It also improved the alterations in brain-derived neurotrophic factor (BDNF) and histopathology induced by reserpine.

CONCLUSIONS

The augmentation of lithium with cerebrolysin showed a clear beneficial effect in the present model of depression suggesting the use of cerebrolysin as an adjuvant in antidepressant treatment.

Short Working Memory Impairment Associated with Hippocampal Microglia Activation in Chronic Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a major neuropsychological condition that occursas a result of impaired liver function. It is frequently observed in patients with advanced liver disease or cirrhosis. Memory impairment is among the symptoms of HE; the pathophysiologic mechanism for this enervating condition remains unclear. However, it is possible that neuroinflammation may be involved, as recent studies have emphasized such phenomena. Therefore, the aim of the present study is to assess short working memory (SWM) and examine the involvement of microglia in a chronic model of HE. The study was carried out with male Wistar rats that were induced by repeated thioacetamide (TAA) administration (100 mg/kg i.p injection for 10 days). SWM function was assessed through Y-maze, T-Maze, and novel object recognition (NOR) tests, together with an immunofluorescence study of microglia activation within the hippocampal areas. Our data showed impaired SWM in TAA-treated rats that was associated with microglial activation in the three hippocampal regions, and which contributed to cognitive impairment.

Sleep deprivation induces late deleterious effects in a pharmacological model of Parkinsonism

Parkinson's disease is a degenerative, chronic and progressive disease, characterized by motor dysfunctions. Patients also exhibit non-motor symptoms, such as affective and sleep disorders. Sleep disorders can potentiate clinical and neuropathological features and lead to worse prognosis. The goal of this study was to evaluate the effects of sleep deprivation (SD) in mice submitted to a progressive pharmacological model of Parkinsonism (chronic administration with a low dose of reserpine). Male Swiss mice received 20 injections of reserpine (0.1 mg/kg) or vehicle, on alternate days. SD was applied before or during reserpine treatment and was performed by gentle handling for 6 h per day for 10 consecutive days. Animals were submitted to motor and non-motor behavioral assessments and neurochemical evaluations. Locomotion was increased by SD and decreased by reserpine treatment. SD during treatment delayed the onset of catalepsy, but SD prior to treatment potentiated reserpine-induced catalepsy. Thus, although SD induced an apparent beneficial effect on motor parameters, a delayed deleterious effect on alterations induced by reserpine was found. In the object recognition test, both SD and reserpine treatment produced cognitive deficits. In addition, the association between SD and reserpine induced anhedonic-like behavior. Finally, an increase in oxidative stress was found in hippocampus of mice subjected to SD, and tyrosine hydroxylase immunoreactivity was reduced in substantia nigra of reserpine-treated animals. Results point to a possible late effect of SD, aggravating the deficits in mice submitted to the reserpine progressive model of PD.

Animal Approaches to Studying Risk Factors for Parkinson's Disease: A Narrative Review

Despite recent efforts to search for biomarkers for the pre-symptomatic diagnosis of Parkinson's disease (PD), the presence of risk factors, prodromal signs, and family history still support the classification of individuals at risk for this disease. Human epidemiological studies are useful in this search but fail to provide causality. The study of well-known risk factors for PD in animal models can help elucidate mechanisms related to the disease's etiology and contribute to future prevention or treatment approaches. This narrative review aims to discuss animal studies that investigated four of the main risk factors and/or prodromal signs related to PD: advanced age, male sex, sleep alterations, and depression. Different databases were used to search the studies, which were included based on their relevance to the topic. Although still in a reduced number, such studies are of great relevance in the search for evidence that leads to a possible early diagnosis and improvements in methods of prevention and treatment.

Transcranial photobiomodulation ameliorates midbrain and striatum neurochemical impairments and behavioral deficits in reserpine-induced parkinsonism in rats

Photobiomodulation (PBM) of deep brain structures through transcranial infrared irradiation might be an effective treatment for Parkinson's disease (PD). However, the mechanisms underlying this intervention should be elucidated to optimize the therapeutic outcome and maximize therapeutic efficacy. The present study aimed at investigating the oxidative stress-related parameters of malondialdehyde (MDA), nitric oxide (NO), and reduced glutathione (GSH) and the enzymatic activities of sodium-potassium-ATPase (Na+, K+-ATPase), Acetylcholinesterase (AChE), and monoamine oxidase (MAO) and monoamine levels (dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the midbrain and striatum of reserpine-induced PD in an animal model treated with PBM. Furthermore, the locomotor behavior of the animals has been determined by the open field test. Animals were divided into three groups; the control group, the PD-induced model group, and the PD-induced model treated with the PBM group. Non-invasive treatment of animals for 14 days with 100 mW, 830 nm laser has demonstrated successful attainment in the recovery of oxidative stress, and enzymatic activities impairments induced by reserpine (0.2 mg/kg) in both midbrain and striatum of adult male Wistar rats. PBM also improved the decrease in DA, NE, and 5-HT in the investigated brain regions. On a behavioral level, animals showed improvement in their locomotion activity. These findings have shed more light on some mechanisms underlying the treatment potential of PBM and displayed the safety, easiness, and efficacy of PBM treatment as an alternative to pharmacological treatment for PD.

Brain Noradrenergic Innervation Supports the Development of Parkinson's Tremor: A Study in a Reserpinized Rat Model

The pathophysiology of tremor in Parkinson's disease (PD) is evolving towards a complex alteration to monoaminergic innervation, and increasing evidence suggests a key role of the locus coeruleus noradrenergic system (LC-NA). However, the difficulties in imaging LC-NA in patients challenge its direct investigation. To this end, we studied the development of tremor in a reserpinized rat model of PD, with or without a selective lesioning of LC-NA innervation with the neurotoxin DSP-4. Eight male rats (Sprague Dawley) received DSP-4 (50 mg/kg) two weeks prior to reserpine injection (10 mg/kg) (DR-group), while seven male animals received only reserpine treatment (R-group). Tremor, rigidity, hypokinesia, postural flexion and postural immobility were scored before and after 20, 40, 60, 80, 120 and 180 min of reserpine injection. Tremor was assessed visually and with accelerometers. The injection of DSP-4 induced a severe reduction in LC-NA terminal axons (DR-group: 0.024 ± 0.01 vs. R-group: 0.27 ± 0.04 axons/um2, p < 0.001) and was associated with significantly less tremor, as compared to the R-group (peak tremor score, DR-group: 0.5 ± 0.8 vs. R-group: 1.6 ± 0.5; p < 0.01). Kinematic measurement confirmed the clinical data (tremor consistency (% of tremor during 180 s recording), DR-group: 37.9 ± 35.8 vs. R-group: 69.3 ± 29.6; p < 0.05). Akinetic-rigid symptoms did not differ between the DR- and R-groups. Our results provide preliminary causal evidence for a critical role of LC-NA innervation in the development of PD tremor and foster the development of targeted therapies for PD patients.

Animal models of Parkinson's disease: bridging the gap between disease hallmarks and research questions

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms. More than 200 years after its first clinical description, PD remains a serious affliction that affects a growing proportion of the population. Prevailing treatments only alleviate symptoms; there is still neither a cure that targets the neurodegenerative processes nor therapies that modify the course of the disease. Over the past decades, several animal models have been developed to study PD. Although no model precisely recapitulates the pathology, they still provide valuable information that contributes to our understanding of the disease and the limitations of our treatment options. This review comprehensively summarizes the different animal models available for Parkinson's research, with a focus on those induced by drugs, neurotoxins, pesticides, genetic alterations, α-synuclein inoculation, and viral vector injections. We highlight their characteristics and ability to reproduce PD-like phenotypes. It is essential to realize that the strengths and weaknesses of each model and the induction technique at our disposal are determined by the research question being asked. Our review, therefore, seeks to better aid researchers by ensuring a concrete discernment of classical and novel animal models in PD research.

Molecular mechanisms underlying the neuroprotection of environmental enrichment in Parkinson's disease

Parkinson's disease is the most common movement disorder, affecting about 1% of the population over the age of 60 years. Parkinson's disease is characterized clinically by resting tremor, bradykinesia, rigidity and postural instability, as a result of the progressive loss of nigrostriatal dopaminergic neurons. In addition to this neuronal cell loss, Parkinson's disease is characterized by the accumulation of intracellular protein aggregates, Lewy bodies and Lewy neurites, composed primarily of the protein α-synuclein. Although it was first described almost 200 years ago, there are no disease-modifying drugs to treat patients with Parkinson's disease. In addition to conventional therapies, non-pharmacological treatment strategies are under investigation in patients and animal models of neurodegenerative disorders. Among such strategies, environmental enrichment, comprising physical exercise, cognitive stimulus, and social interactions, has been assessed in preclinical models of Parkinson's disease. Environmental enrichment can cause structural and functional changes in the brain and promote neurogenesis and dendritic growth by modifying gene expression, enhancing the expression of neurotrophic factors and modulating neurotransmission. In this review article, we focus on the current knowledge about the molecular mechanisms underlying environmental enrichment neuroprotection in Parkinson's disease, highlighting its influence on the dopaminergic, cholinergic, glutamatergic and GABAergic systems, as well as the involvement of neurotrophic factors. We describe experimental pre-clinical data showing how environmental enrichment can act as a modulator in a neurochemical and behavioral context in different animal models of Parkinson's disease, highlighting the potential of environmental enrichment as an additional strategy in the management and prevention of this complex disease.

Effects of graphene oxide nanoparticles administration against reserpine-induced neurobehavioral damage and oxidative stress in an animal model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the degeneration of substantia nigra dopaminergic neurons. Many therapeutic strategies were explored for PD with no success. In this study, we investigated the efficacy of graphene oxide nanoparticles (GONPs) using the reserpine model of PD. Low concentrations GONPs were utilized as a therapeutic agent in many neurodegenerative diseases. We assessed the neurobehavioral alterations in the reserpine model of PD and investigated the neuroprotective and antioxidant effects of GONPs in this model. Thirty male mice were separated into three groups (N = 10): C (control); Res (Reserpine 0.25 mg/kg); Res + GONPs (Reserpine 0.25 mg/kg and GONPs 25 mg/kg). Our results showed that reserpine neurotoxicity induced hypoactivity with a significant increase of superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) levels in the brain and brainstem. GONPs reversed the reserpine-induced hypoactivity concomitant with decreased neuronal CAT and MDA levels. These findings support the potential use of GONPs as an antioxidant agent in the central nervous system (CNS) that protects against neurodegeneration in the reserpine PD model.

L-DOPA Improves Ventilation but Not the Ventilatory Response to Hypercapnia in a Reserpine Model of Parkinson's Disease

Parkinson's disease (PD) is a neurological disorder characterized by progressive degeneration of the substantia nigra that affects mainly movement control. However, pathological changes associated with the development of PD may also alter respiration and can lead to chronic episodes of hypoxia and hypercapnia. The mechanism behind impaired ventilation in PD is unclear. Therefore, in this study, we explore the hypercapnic ventilatory response in a reproducible reserpine-induced (RES) model of PD and parkinsonism. We also investigated how dopamine supplementation with L-DOPA, a classic drug used to treat PD, would affect the breathing and respiratory response to hypercapnia. Reserpine treatment resulted in decreased normocapnic ventilation and behavioral changes manifested as low physical activity and exploratory behavior. The respiratory rate and the minute ventilation response to hypercapnia were significantly higher in sham rats compared to the RES group, while the tidal volume response was lower. All of this appears to be due to reduced baseline ventilation values produced by reserpine. L-DOPA reversed reduced ventilation, indicating a stimulatory effect of DA on breathing, and showed the potency of DA supplementation in restoring normal respiratory activity.

Genetic effects in a progressive model of parkinsonism induced by reserpine

OBJECTIVE AND METHODS

We investigated the locomotor, emotional, physiological, and neurobiological effects induced by low-dose reserpine repeated treatment (0.1 mg/kg; 14 injections) in males from the Lewis (LEW), Spontaneously Hypertensive Rats (SHR), and SHR.LEW-(D4Rat76-D4Mgh11) (SLA16) isogenic rat strains, which have different genetic backgrounds on chromosome 4. Behavioral responses in the catalepsy, open-field, and oral movements' tests were coupled with blood pressure, body weight, and striatal tyrosine hydroxylase (TH) level assessments to establish neurobiological comparisons between reserpine-induced impairments and genetic backgrounds RESULTS: Results revealed the SHR strain was more sensitive in the catalepsy test and exhibited higher TH immunoreactivity in the dorsal striatum. The SLA16 strain presented more oral movements, suggesting increased susceptibility to develop oral dyskinesia.

CONCLUSIONS

Our results showed the efficacy of repeated treatment with a low dose of reserpine and demonstrated, for the first time, the genetic influence of a specific region of chromosome 4 on the expression of these effects.

Evaluation of the therapeutic potential of cerebrolysin and/or lithium in the male Wistar rat model of Parkinson's disease induced by reserpine

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease worldwide and represents a challenge for clinicians. The present study aims to investigate the effects of cerebrolysin and/or lithium on the behavioral, neurochemical and histopathological alterations induced by reserpine as a model of PD. The rats were divided into control and reserpine-induced PD model groups. The model animals were further divided into four subgroups: rat PD model, rat PD model treated with cerebrolysin, rat PD model treated with lithium and rat PD model treated with a combination of cerebrolysin and lithium. Treatment with cerebrolysin and/or lithium ameliorated most of the alterations in oxidative stress parameters, acetylcholinesterase and monoamines in the striatum and midbrain of reserpine-induced PD model. It also ameliorated the changes in nuclear factor-kappa and improved the histopathological picture induced by reserpine. It could be suggested that cerebrolysin and/or lithium showed promising therapeutic potential against the variations induced in the reserpine model of PD. However, the ameliorating effects of lithium on the neurochemical, histopathological and behavioral alterations induced by reserpine were more prominent than those of cerebrolysin alone or combined with lithium. It can be concluded that the antioxidant and anti-inflammatory effects of both drugs played a significant role in their therapeutic potency.

Botulinum neurotoxin A ameliorates depressive-like behavior in a reserpine-induced Parkinson's disease mouse model via suppressing hippocampal microglial engulfment and neuroinflammation

Depression is one of the common non-motor symptoms of Parkinson's disease (PD). In the clinic, botulinum neurotoxin A (BoNT/A) has been used to treat depression. In this study, we investigated the mechanisms underlying the anti-depressive effect of BoNT/A in a PD mouse model. Mice were administered reserpine (3 μg/mL in the drinking water) for 10 weeks. From the 10^th week, BoNT/A (10 U·kg^-1·d^-1) was injected into the cheek for 3 consecutive days. We showed that chronic administration of reserpine produced the behavioral phenotypes of depression and neurochemical changes in the substantia nigra pars compacta (SNpc) and striatum. BoNT/A treatment significantly ameliorated the depressive-like behaviors, but did not improve TH activity in SNpc of reserpine-treated mice. We demonstrated that BoNT/A treatment reversed reserpine-induced complement and microglia activation in the hippocampal CA1 region. Furthermore, BoNT/A treatment significantly attenuated the microglial engulfment of presynaptic synapses, thus ameliorating the apparent synapse and spine loss in the hippocampus in the reserpine-treated mice. Moreover, BoNT/A treatment suppressed microglia-mediated expression of pro-inflammatory cytokines TNF-α and IL-1β in reserpine-treated mice. In addition, we showed that BoNT/A (0.1 U/mL) ameliorated reserpine-induced complement and microglia activation in mouse BV2 microglial cells in vitro. We conclude that BoNT/A ameliorates depressive-like behavior in a reserpine-induced PD mouse model through reversing the synapse loss mediated by classical complement induced-microglial engulfment as well as alleviating microglia-mediated proinflammatory responses. BoNT/A ameliorates depressive-like behavior, and reverses synapse loss mediated by classical complement pathway-initiated microglia engulfment as well as alleviates microglia-mediated proinflammatory response in the reserpine-induced Parkinson's disease mouse model.

Alpha-lipoic acid-role in improving both reserpine toxicity and paroxetine treatment in the cerebral cortex of albino rats; histological, ultrastructural, immunohistohemical and biochemical studies

Background

Reserpine is a monoamine depletory drug cause oxidative damage and used to induce depression-like features in rodent model. Paroxetine is an antidepressant drug that exerts its effects by inhibiting dopaminergic neurons although it may exert much pathological damage. Alpha-lipoic acid (ALA) is an endogenous antioxidant co-factor of important enzymatic complexes. The present study was aimed to elucidate the possible protective effect of ALA in the improvement of the deleterious cerebral cortex injury after reserpine and paroxetine treatment. Forty adult male albino rats were equally divided into 5 groups. Group I served as control group orally treated with saline solution all the experiment period. Group II animals orally treated with ALA (200 mg/kg/day) for six weeks. The induction of depression-like features occurred when the rest of animals were intraperitoneally treated with 25 mg/kg of reserpine once daily for consecutive 14 day. Then these animals were divided into; Group III (reserpine group) animals in this group were sacrificed on 15th day. Group IV; reserpine-treated animals were treated with paroxetine (20 mg/kg) daily for 6 weeks. Group V, animals in this group were received paroxetine and ALA daily for 6 weeks.

Results

Reserpine-treated rats showed disorganized layers of cerebral cortex with degenerative, apoptotic and necrotic changes. Ultrastructure changes include both pyramidal and granule cells with severe degenerative, necrotic and apoptotic features. The nuclei appeared pyknotic; irregular with chromatin condensation as well as the cytoplasm of these cells contained many degenerated organelles. In addition, a significant increase in total oxidative stress and decrease in total antioxidant capacity, norepinephrine, dopamine and serotonin levels were recorded. The same treatment showed significant decrease in proliferating cell nuclear antigen (PCNA) expression and significant increase in caspase-3 expression in the granule and pyramidal cells. After paroxetine-treatment these parameters were more or less similar to those observed in reserpine-treated ones. While an obvious improvement was appeared when animal treated with both paroxetine and ALA and; all parameters restored its normal features.

Conclusions

This study concluded that; ALA treatment attenuated the cerebral injury induced by reserpine and improved the effects of paroxetine in rats due to its anti-inflammatory, anti-apoptotic and antioxidant activities.

Preclinical reserpine models recapitulating motor and non-motor features of Parkinson’s disease: Roles of epigenetic upregulation of alpha-synuclein and autophagy impairment

Reserpine is an effective drug for the clinical treatment of hypertension. It also induces Parkinson’s disease (PD)-like symptoms in humans and animals possible through the inhibition of monoamine vesicular transporters, thus decreasing the levels of monoamine neurotransmitters in the brain. However, the precise mechanisms remain unclear. Herein, we aimed to develop a preclinical reserpine model recapitulating the non-motor and motor symptoms of PD and investigate the underlying potential cellular mechanisms. Incubation of reserpine induced apoptosis, led to the accumulation of intracellular reactive oxygen species (ROS), lowered DNA methylation of alpha-synuclein gene, resulted in alpha-synuclein protein deposition, and elevated the ratio of LC3-II/LC3-Ⅰ and p62 in cultured SH-SY5Y cells. Feeding reserpine dose-dependently shortened the lifespan and caused impairment of motor functions in male and female Drosophila. Moreover, long-term oral administration of reserpine led to multiple motor and non-motor symptoms, including constipation, pain hypersensitivity, olfactory impairment, and depression-like behaviors in mice. The mechanistic studies showed that chronic reserpine exposure caused hypomethylation of the alpha-synuclein gene and up-regulated its expression and elevated the ratio of LC3-II/LC3-Ⅰ and expression of p62 in the substantia nigra of mice. Thus, we established preclinical animal models using reserpine to recapitulate the motor and non-motor symptoms of PD. Chronic reserpine exposure epigenetically elevated the levels of alpha-synuclein expression possible by lowering the DNA methylation status and inducing autophagic impairment in vitro and in vivo.

Lippia grata essential oil complexed with β-cyclodextrin ameliorates biochemical and behavioral deficits in an animal model of progressive parkinsonism

Parkinson's disease (PD) is identified by the loss of dopaminergic neurons in the Substantia Nigra pars compacta (SNpc), and is correlated to aggregates of proteins such as α-synuclein, Lewy's bodies. Although the PD etiology remains poorly understood, evidence suggests a main role of oxidative stress on this process. Lippia grata Schauer, known as "alecrim-do-mato", "alecrim-de-vaqueiro", "alecrim-da-chapada", is a native bush from tropical areas mainly distributed throughout the Central and South America. This plant species is commonly used in traditional medicine for relief of pain and inflammation conditions, and that has proven antioxidant effects. We evaluated the effects of essential oil of the L. grata after its complexed with β-cyclodextrin (LIP) on PD animal model induced by reserpine (RES). Behavioral assessments were performed across the treatment. Upon completion the treatment, the animals were euthanized, afterwards their brains were isolated and processed for immunohistochemical and oxidative stress analysis. The LIP treatment delayed the onset of the behavior of catalepsy, decreased the number of oral movements and prevented the memory impairment on the novel object recognition task. In addition, the treatment with LIP protected against dopaminergic depletion in the SNpc and dorsal striatum (STRd), and decreased the α-syn immunoreactivity in the SNpc and hippocampus (HIP). Moreover, there was reduction of the oxidative stability index. These findings demonstrated that the LIP treatment has neuroprotective effect in a progressive parkinsonism model, suggesting that LIP could be an important source for novel treatment approaches in PD.

Aging accentuates decrease in tyrosine hydroxylase immunoreactivity associated with the increase in the motor impairment in a model of reserpine-induced parkinsonism

Parkinson's disease (PD) is an age-related neurodegenerative disorder characterized by progressive dopaminergic neuron loss. Animal models have been used to develop a better understanding of the pathophysiologic mechanisms of PD. However, these models are usually conducted with young animals diverging of the age of PD patients, suggesting a bias in translational science. Thus, the aim of the study was to evaluate the effect of the age on rats in a progressive parkinsonism model induced by reserpine (RES). Adult (6 - 8 month-old) or elderly (18 - 24 month-old) male rats were assigned to six groups: control-elderly (CTL-ELDERLY), reserpine-elderly (RES-ELDERLY), reserpine-elderly withdrawal (RES-ELDERLY WITHDRAWAL), control-adult (CTL-ADULT), reserpine-adult (RES-ADULT), and reserpine-adult withdrawal (RES-ADULT WITHDRAWAL). Animals received 15 injections every other day of RES (0.1 mg / kg) or vehicle during 30 days. Throughout treatment, animals were evaluated in the catalepsy test (every 48 h) and open field test (24 h after the second injection), and weight assessment (every 4 days) was also made. Upon completion of behavioral tests, rat brains were collected for tyrosine hydroxylase (TH) immunohistochemical analysis. Main results demonstrated that RES-treated animals spent more time in the catalepsy bar compared with control groups, moreover the RES-elderly group showed a longer catalepsy time compared with the RES-ADULT group. A shorter time from RES treatment to the development of symptoms was observed in the RES-ADULT group, compared with the RES-ELDERLY group. In addition, RES-induced weight loss in both RES-ELDERLY and RES-ADULT when compared with their corresponding controls. Cessation of RES treatment was followed by weight gain only in the RES-ADULT group. A significant decrease in TH-immunoreactive cells was observed in the substantia nigra pars compacta (SNpc) and dorsal striatum (STR) in the rats in both the RES-ADULT and RES-ELDERLY groups and in the ventral tegmental area in rats in the RES-ADULT group. Furthermore, TH immunoreactivity decrease was not reversible in SNpc and STR in the RES-ELDERLY. These results show that RES has an age-dependent effect in rats, suggesting a greater sensitivity of the dopaminergic pathway to RES with advancing age. These suggest that the RES rat model of parkinsonism can be useful in improving our knowledge on the effect of aging on neurodegeneration.

Neuroinflammation in early, late and recovery stages in a progressive parkinsonism model in rats

Parkinson’s disease (PD) is characterized by motor and non-motor signs, which are accompanied by progressive degeneration of dopaminergic neurons in the substantia nigra. Although the exact causes are unknown, evidence links this neuronal loss with neuroinflammation and oxidative stress. Repeated treatment with a low dose of reserpine—inhibitor of VMAT2—has been proposed as a progressive pharmacological model of PD. The aim of this study was to investigate whether this model replicates the neuroinflammation characteristic of this disease. Six-month-old Wistar rats received repeated subcutaneous injections of reserpine (0.1 mg/kg) or vehicle on alternate days. Animals were euthanized after 5, 10, or 15 injections, or 20 days after the 15th injection. Catalepsy tests (motor assessment) were conducted across treatment. Brains were collected at the end of each treatment period for immunohistochemical and RT-PCR analyzes. Reserpine induced a significant progressive increase in catalepsy duration. We also found decreased immunostaining for tyrosine hydroxylase (TH) in the substantia nigra pars compacta (SNpc) and increased GFAP + cells in the SNpc and dorsal striatum after 10 and 15 reserpine injections. Phenotyping microglial M1 and M2 markers showed increased number of CD11b + cells and percentage of CD11b + /iNOS + cells in reserpine-treated animals after 15 injections, which is compatible with tissue damage and production of cytotoxic factors. In addition, increased CD11b + /ArgI + cells were found 20 days after the last reserpine injection, together with an increment in IL-10 gene expression in the dorsal striatum, which is indicative of tissue repair or regeneration. Reserpine also induced increases in striatal interleukin TNF-alpha mRNA levels in early stages. In view of these results, we conclude that reserpine-induced progressive parkinsonism model leads to neuroinflammation in regions involved in the pathophysiology of PD, which is reversed 20 days after the last injection. These findings reveal that withdrawal period, together with the shift of microglial phenotypes from the pro-inflammatory to the anti-inflammatory stage, may be important for the study of the mechanisms involved in reversing this condition, with potential clinical applicability.

Effects of obesity on neuroinflammatory and neurochemical parameters in an animal model of reserpine-induced Parkinson's disease

Obesity is associated with low-grade chronic inflammation and oxidative stress, affecting the brain's reward system by decreasing dopaminergic neurotransmission. It is known that dopaminergic neurotransmission is also reduced in Parkinson's disease (PD), and high adiposity is considered a risk factor for the development of several neurodegenerative diseases, including PD. This study aimed to assess the effects of obesity on neuroinflammatory and neurochemical parameters in an animal model of reserpine-induced PD. The obese group showed increased inflammation and oxidative damage as well as inhibition of mitochondrial respiratory chain complexes I and II and DNA damage in the evaluated structures. The PD group did not show inflammation or mitochondrial dysfunction but exhibited oxidative damage in the hippocampus. The combination group (obesity + PD) showed reduced inflammation and oxidative stress and increased activity of complexes I and II of the mitochondrial respiratory chain in most of the analyzed structures. On the other hand, obesity + PD caused oxidative damage to proteins in the liver, prefrontal cortex, striatum, and cerebral cortex and oxidative stress in the hypothalamus, resulting in reduced catalase activity. Furthermore, the combination group showed DNA damage in blood, liver, and cerebral cortex. In conclusion, it was observed that the association of obesity and PD did not increase inflammation, oxidative stress, or mitochondrial dysfunction in most of the evaluated structures but increased oxidative damage and induced mechanisms that led to DNA damage in peripheral tissues and brain structures.

Rodent models for gait network disorders in Parkinson's disease - a translational perspective

Gait impairments in Parkinson's disease remain a scientific and therapeutic challenge. The advent of new deep brain stimulation (DBS) devices capable of recording brain activity from chronically implanted electrodes has fostered new studies of gait in freely moving patients. The hope is to identify gait-related neural biomarkers and improve therapy using closed-loop DBS. In this context, animal models offer the opportunity to investigate gait network activity at multiple biological scales and address unresolved questions from clinical research. Yet, the contribution of rodent models to the development of future neuromodulation therapies will rely on translational validity. In this review, we summarize the most effective strategies to model parkinsonian gait in rodents. We discuss how clinical observations have inspired targeted brain lesions in animal models, and whether resulting motor deficits and network oscillations match recent findings in humans. Gait impairments with hypo-, bradykinesia and altered limb rhythmicity were successfully modelled in rodents. However, clear evidence for the presence of freezing of gait was missing. The identification of reliable neural biomarkers for gait impairments has remained challenging in both animals and humans. Moving forward, we expect that the ongoing investigation of circuit specific neuromodulation strategies in animal models will lead to future optimizations of gait therapy in Parkinson's disease.

Motor, memory, and anxiety-like behavioral impairments associated with brain-derived neurotrophic factor and dopaminergic imbalance after inhalational exposure to deltamethrin

Believed to cause damage to the nervous system and possibly being associated with neurodegenerative diseases, deltamethrin (DM) is a type II pyrethroid used in pest control, public health, home environment, and vector control. The objective of this study was to evaluate the motor, cognitive and emotional changes associated with dopaminergic and BDNF imbalance after DM exposure in rats. Sixty Wistar rats (9-10 months-old) were used, under Ethics Committee on Animal Research license (ID 19/2017). The animals were randomly divided into four groups: control (CTL, 0.9% saline), DM2 (2mg DM in 1.6mL 0.9% saline), DM4 (4mg of DM in 1.6mL of 0.9% saline), and DM8 (8mg of DM in 1.6mL of 0.9% saline). DM groups were submitted to 9 or 15 inhalations, one every 48hours. Half of the animals from each group were randomly selected and perfused 24hours after the 9th or 15th inhalation. Throughout the experiment, the animal's behavior were evaluated using catalepsy test, open field, hole-board test, Modified Elevated Plus Maze, and social interaction. At the end of the experiments, the rats were perfused transcardially and their brains were processed for Tyrosine Hydroxylase (TH) and Brain derived neurotrophic factor (BDNF) immunohistochemistries. The animals submitted to 9 inhalations of DM showed a reduction in immunoreactivity for TH in the Substantia nigra pars compacta (SNpc), ventral tegmental area (VTA), and dorsal striatum (DS) areas, and an increase in BDNF in the DS and CA1, CA3 and dentate gyrus (DG) hippocampal areas. Conversely, the animals submitted to 15 inhalations of DM showed immunoreactivity reduced for TH in the SNpc and VTA, and an increase in BDNF in the hippocampal areas (CA3 and DG). Our results indicate that the DM inhalation at different periods induce motor and cognitive impairments in rats. Such alterations were accompanied by dopaminergic system damage and a possible dysfunction on synaptic plasticity.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

Female Rats Are Resistant to Cognitive, Motor and Dopaminergic Deficits in the Reserpine-Induced Progressive Model of Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease. The main symptoms are motor signs such as resting tremor and difficulty in initializing movements. Non-motor alterations, such as cognitive deficits, can precede the motor symptoms. PD is more frequent in men than women. The mechanisms related to this difference are not completely understood. There is evidence that females present distinct characteristics in dopaminergic function compared to males. While the severity of motor impairments is often compared between sexes, little is known about sex differences in the prodromal stage. Most animal models of PD present acute severe motor impairment, which precludes the study of non-motor symptoms. Our research group have proposed an adaptation of the classic reserpine protocol, using low doses in a chronic treatment. This method allows the observation of progressive motor impairment as well as premotor deficits. Here we investigate possible behavioral and neuronal sex differences in the effects of the repeated treatment with a low dose of reserpine in rats. Male and female Wistar rats received 10–15 injections of reserpine (0.1 mg/kg) or vehicle, on alternate days. We followed-up the estrous cycle phases and conducted motor and cognitive assessments (catalepsy, open field, oral movements and object recognition tests). The euthanasia occurred 48 h after the 10th or 15th injections, with the collection of blood for the quantification of sex hormones and brains for tyrosine hydroxylase (TH) immunohistochemistry in the substantia nigra pars compact (SNpc). Reserpine induced progressive catalepsy, involuntary oral movements and cognitive deficits in male rats. The behavioral effects of reserpine were attenuated (motor) or absent (cognitive) in females. Reserpine decreased TH immunoreactivity in males, but not in females. Estrogen levels in females negatively correlated with catalepsy duration. Our findings show that females present a delay and/or a prevention in the reserpine-induced motor alterations in the progressive PD model, compatible with the lower prevalence of this disease in women. Further, females were protected from the deficit in object recognition at the prodromal stage. The absence of reserpine-induce decrease in TH immunoreactivity suggests that differences in dopaminergic function/plasticity are related to this protection in female sex.

Neonatal Reserpine Administration Produces Widespread Neuronal Losses and ⍺-Synuclein Inclusions in a Rat Model

Historically, reserpine was widely used as an antihypertensive drug. However, severe motor and non-motor symptoms such as dyskinesia and depression led to the discontinuation of reserpine as a first-line treatment for hypertension. Reserpine functions by inhibiting vesicular monoamine transporter 2 (VMAT2), reducing sequestration of monoamines into synaptic vesicles. The consequent reduction in monoamines, most notably dopamine, serotonin and norepinephrine, in the central nervous system, causes well-defined symptoms such as catalepsy, hypoactivity and sedation in animals, and these motor and non-motor symptoms are well defined for reserpine treatment. However, no gross neuropathological changes in response to reserpine treatment have been reported previously in any animal model. In contrast, reducing VMAT2 expression in genetically modified VMAT2 LO mice leads to the production of ⍺-synuclein-positive aggregates and progressive nigrostriatal neuronal loss. These VMAT2 LO mice have reduced VMAT2 functionality during critical brain developmental stages and this could be the key to producing a reserpine model with matching histopathologies. The aim of this study was therefore to investigate the effect of neonatal reserpine administration on brain histology. We report here that a single dose of 5 mg kg^-1 reserpine administered subcutaneously to neonatal rats on postnatal day 3 leads to widespread neuronal loss in various brain regions including the substantia nigra pars compacta, ventral tegmental area, striatum, hippocampus, locus coeruleus, amygdala and cerebral cortex, and the presence of ⍺-synuclein-positive inclusions in the substantia nigra pars compacta and the dorsal striatum within 30 days of administration.

Neuroprotective effect of α-pinene self-emulsifying nanoformulation against 6-OHDA induced neurotoxicity on human SH-SY5Y cells and its in vivo validation for anti-Parkinson's effect

Oxidative stress (OS) is involved in the multifaceted pathogenic paradigm of neurodegenerative diseases like Parkinson's disease (PD). Monoterpenes like α-pinene (ALP) is considered to be a therapeutically potent antioxidant agent able to attenuate and scavenge various reactive oxygen species and reactive nitrogen species. The present study aimed to evaluate the in vitro and in vivo neuroprotective effect of α-pinene self-emulsifying nanoformulation (ALP-SENF) for PD. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay was done to evaluate the neurotoxic dose of the ALP-SENF; however, the neuroprotective effect was assessed by 6-hydroxydopamine (6-OHDA) induced neurotoxicity model on SH-SY5Y taking NAC (N-acetyl-l-cysteine) as standard. The in vivo anti-Parkinson's activity of the ALP-SENF was compared with that of the plain ALP suspension by using reserpine antagonism and haloperidol-induced Parkinsonism model in rats. Various behavioral tests and biochemical antioxidant enzymes were estimated. The in vitro results revealed that treatment with ALP-SENF at a concentration of 100 and 200 µM was found to show significant neuronal SH-SY5Y cell viability against 50 µM 6-OHDA. ALP-SENF treated animals have seen significant neurobehavioral improvement. Furthermore, the levels of antioxidative enzymes in biochemical test reveals a marked enhancement in the expression of antioxidant enzymes that significantly attenuated the OS induced neurodegeneration. Due to the mechanisms of their antioxidant action, it was probably due to the scavenging of free radicals and the expression of antioxidant enzymes. It also improved neurobehavioral changes induced by reserpine and haloperidol.

Myrtenol complexed with β-cyclodextrin ameliorates behavioural deficits and reduces oxidative stress in the reserpine-induced animal model of Parkinsonism

Current pharmacological approaches to treat Parkinson's disease have low long-term efficacy and important adverse side effects. The development of new pharmacological therapies has focused on novel plant-derived phytochemicals. The alcoholic monoterpene myrtenol has been isolated from several plant species, and has anxiolytic, analgesic, anti-inflammatory and antioxidant actions. Our study evaluated the neuroprotective potential of myrtenol complexed with β-cyclodextrin (MYR) on a progressive parkinsonism model induced by reserpine (RES) in mice. The complexation with cyclodextrins enhances the pharmacological action of monoterpenes. Male Swiss mice were treated daily with MYR (5 mg/kg, p.o.) and with RES (0.1 mg/kg, s.c.) every other day during 28 days. Behavioural evaluations were conducted across treatment. At the end of the treatment, immunohistochemistry for tyrosine hydroxylase (TH) and oxidative stress parameters were evaluated. Chronic MYR-treatment protected against olfactory sensibility loss, restored short-term memory and decreased RES-induced motor impairments. Moreover, this treatment prevented dopaminergic depletion and reduced the oxidative status index in the dorsal striatum. Therefore, MYR ameliorated motor and non-motor impairments in the progressive animal model of parkinsonism, possibly by an antioxidant action. Additional research is needed to investigate the mechanisms involved in this neuroprotective effect.

Changes in the mesocorticolimbic pathway after low dose reserpine-treatment in Wistar and Spontaneously Hypertensive Rats (SHR): Implications for cognitive deficits in a progressive animal model for Parkinson's disease

Reserpine (RES) is an irreversible inhibitor of VMAT2 used to study Parkinson's disease (PD) and screening for antiparkinsonian treatments in rodents. Recently, the repeated treatment with a low dose of reserpine was proposed as a model capable of emulating progressive neurochemical, motor and non-motor impairments in PD. Conversely, compared to Wistar rats, Spontaneously Hypertensive Rats (SHR) are resistant to motor changes induced by repeated treatment with a low dose of RES. However, such resistance has not yet been investigated for RES-induced non-motor impairments. We aimed to assess whether SHR would have differential susceptibility to the object recognition deficit induced by repeated low-dose reserpine treatment. We submitted male Wistar and SHR rats to repeated RES treatment (15 s.c. injections of 0.1 mg/kg, every other day) and assessed object memory acquisition and retrieval 48 h after the 6^th RES injection (immediately before the appearance of motor impairments). Only RES Wistar rats displayed memory impairment after reserpine treatment. On the other hand, untreated SHR rats displayed object recognition memory deficit, but RES treatment restored such deficits. We also performed immunohistochemistry for tyrosine hydroxylase (TH) and α-synuclein (α-syn) 48 h after the last RES injection. In a different set of animals submitted to the same treatment, we quantified DA, 5-HT and products of lipid peroxidation in the prefrontal cortex (PFC) and hippocampus (HPC). SHR presented increased constitutive levels of DA in the PFC and reduced immunoreactivity to TH in the medial PFC and dorsal HPC. Corroborating the behavioral findings, RES treatment restored those constitutive alterations in SHR. These findings indicate that the neurochemical, molecular and genetic differences in the SHR strain are potentially relevant targets to the study of susceptibility to diseases related to dopaminergic alterations.

Nociception alterations precede motor symptoms in a progressive model of parkinsonism induced by reserpine in middle-aged rats

Nociception alterations are frequent non-motor symptoms of the prodromal phase of Parkinson's disease (PD). The period for the onset of symptoms and the pathophysiological mechanisms underlying these alterations remain unclear. We investigated the course of nociception alterations in a progressive model of parkinsonism induced by reserpine (RES) in rats. Male Wistar rats (6-7 months) received 5 or 10 subcutaneous injections of RES (0.1 mg/kg) or vehicle daily for 20 days. Motor evaluation and nociceptive assessment were performed throughout the treatment. At the end of the treatment rats were euthanized, the brains removed and processed for immunohistochemical analysis (TH and c-Fos). The RES-treated rats exhibited an increased nociceptive response to mechanical and chemical stimulation in the electronic von Frey and formalin tests, respectively. Moreover, these alterations preceded the motor impairment observed in the catalepsy test. In addition, the RES treatment reduced the TH-immunoreactivity in the ventral tegmental area (VTA) and increased the c-Fos expression in the ventral-lateral periaqueductal gray (vlPAG), rostral ventral medulla (RVM) and dorsal raphe nucleus (DRN) after noxious stimuli induced by formalin. Taken together, our results reinforce that nociceptive changes are one of the early signs of PD and monoamine depletion in basal ganglia can be involved in the abnormal processing of nociceptive information in PD.

Deficiency of Biogenic Amines Modulates the Activity of Hypoglossal Nerve in the Reserpine Model of Parkinson's Disease

The underlying cause of respiratory impairments appearing in Parkinson's disease (PD) is still far from being elucidated. To better understand the pathogenesis of respiratory disorders appearing in PD, we studied hypoglossal (HG) and phrenic (PHR) motoneuron dysfunction in a rat model evoked with reserpine administration. After reserpine, a decrease in the baseline amplitude and minute HG activity was noted, and no depressive phase of the hypoxic ventilatory response was observed. The pre-inspiratory time of HG activity along with the ratio of pre-inspiratory time to total respiratory cycle time and the ratio of pre-inspiratory to inspiratory amplitude were significantly reduced during normoxia, hypoxia, and recovery compared to sham rats. We suggest that the massive depletion of not only dopamine, but above all noradrenaline and serotonin in the brainstem observed in our study, has an impact on the pre-inspiratory activity of the HG. The shortening of the pre-inspiratory activity of the HG in the reserpine model may indicate a serious problem with maintaining the correct diameter of the upper airways in the preparation phase for inspiratory effort and explain the development of obstructive sleep apnea in some PD patients. Therapies involving the supplementation of amine depletion other than dopamine should be considered.

Balance alterations and reduction of pedunculopontine cholinergic neurons in early stages of parkinsonism in middle-aged rats

The purpose of the present study was to investigate balance alterations and the possible role of the cholinergic neurons in the pedunculopontine nucleus (PPN) in the early stages of a progressive animal model of Parkinson's disease (PD). Twenty-eight middle-aged (8-9 months) male Wistar rats received 4 or 10 subcutaneous vehicle (control, CTL) or reserpine (RES) injections (0.1 mg/kg). The animals were submitted to different behavioral tests. Forty-eight hours after the 4th injection, half of the animals of each group (n = 7) were perfused and submitted to immunohistochemical analysis for tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT). The remaining animals (n = 7 per group) were killed 48 h after the 10th injection. RES group presented motor deficits in the catalepsy and open field tests starting at days 12 and 20 of treatment, respectively (only for the animals that received 10 injections). On the other hand, dynamic and static balance changes were observed at earlier stages of RES treatment, starting at days 6 and 4, respectively. At this point of the treatment, there was no decrease in the number of TH immunoreactivity neurons in the substantia nigra pars compacta (SNpc), ventral tegmental area (VTA) and dorsal striatum (DS). However, a decrease was observed in SNpc and dorsal striatum of animals that received 10 injections. In contrast, there was a decrease in the number of ChAT immunoreactive cells in PPN concomitantly to the balance alterations at the early stages of treatment (after 4 RES injections). Thus, by mimicking the progressiveness of PD, the reserpine model made it possible to identify static and dynamic balance impairments prior to the motor alterations in the catalepsy and open field tests. In addition, changes in balance were accompanied by a reduction in the number of ChAT immunoreactive cells in NPP in the early stages of treatment.

Caffeine: An Overview of Its Beneficial Effects in Experimental Models and Clinical Trials of Parkinson's Disease

Parkinson’s Disease (PD) is a neurological disease characterized by the progressive degeneration of the nigrostriatal dopaminergic pathway with consequent loss of neurons in the substantia nigra pars compacta and dopamine depletion. The cytoplasmic inclusions of α-synuclein (α-Syn), known as Lewy bodies, are the cytologic hallmark of PD. The presence of α-Syn aggregates causes mitochondrial degeneration, responsible for the increase in oxidative stress and consequent neurodegeneration. PD is a progressive disease that shows a complicated pathogenesis. The current therapies are used to alleviate the symptoms of the disease without changing its clinical course. Recently, phytocompounds with neuroprotective effects and antioxidant properties such as caffeine have aroused the interest of researchers. The purpose of this review is to summarize the preclinical studies present in the literature and clinical trials recorded in ClinicalTrial.gov, aimed at illustrating the effects of caffeine used as a nutraceutical compound combined with the current PD therapies. Therefore, the preventive effects of caffeine in the neurodegeneration of dopaminergic neurons encourage the use of this alkaloid as a supplement to reduce the progress of the PD.

Impact of rasagiline nanoparticles on brain targeting efficiency via gellan gum based transdermal patch: A nanotheranostic perspective for Parkinsonism

Rasagiline mesylate is used as first line agent for early management of Parkinson's disease but its water soluble nature creates hurdles to cross blood brain barrier also its low oral bioavailability and rapid elimination requires frequent dosing. Thus present study aims to prepare rasagiline mesylate-nanoparticles (RM-NPs) loaded gellan gum transdermal film for non-invasive; self-administration in elderly patients. PLGA coated RM-NPs prepared by solvent evaporation technique were incorporated into film prepared by solvent casting method. Optimized films with 1.127 g gellan gum and 1.962 % linoleic acid showed enhanced ex-vivo diffusion over a period of 72 h. Comparative pharmacokinetic study revealed increased bioavailability of rasagiline on transdermal application compared to oral route. In-vivo anti-Parkinson activity estimated by behavioural and biochemical analysis indicate reserpine to interfere with monoamine storage hence resulting in development of akinesia and PD-like symptoms in rats. Brain targeting monitored by gamma imaging showed effective brain drug uptake from transdermal film which was also supported by increased brain targeting efficiency estimated from biodistribution study. Thus, the data support efficacy of gellan gum film to target drug to brain region compared to oral route and hence can be employed as a convenient approach for long-term treatment of Parkinson's disease in elderly patients.

Predictions of cognitive detriments from galactic cosmic ray exposures to astronauts on exploration missions

For the first-time we report on predictions on cognitive detriments from galactic cosmic ray (GCR) exposures on long-duration space missions outside the protection of the Earth's magnetosphere and solid body shielding. Estimates are based on a relative risk (RR) model of the fluence response for proton and heavy ion in rodent studies using the widely used novel object recognition (NOR) test, which estimates detriments in recognition or object memory. Our recent meta-analysis showed that linear and linear-quadratic dose response models were not accurate, while exponential increasing fluence response models based on particle track structure provided good descriptions of rodent data for doses up to 1 Gy. Using detailed models of the GCR environment and particle transport in shielding and tissue, we predict the excess relative risk (ERR) for NOR detriments for several long-term space mission scenarios. Predictions suggest ERR < 0.15 for most space mission scenarios with ERR<0.1 for 1-year lunar surface missions, and about ERR~0.1 for a 1000 day Mars mission for average solar cycle conditions. We discuss possible implications of these ERR levels of cognitive performance detriments relative to other neurological challenges such as rodent models of Alzheimer's disease (AD), Parkinson's disease (PD) and traumatic brain injury (TBI). Comparisons suggest a small but potentially clinically significant risk for possible space mission scenarios.

Si-Ni-San Prevents Reserpine-Induced Depression by Inhibiting Inflammation and Regulating CYP450 Enzymatic Activity

Depression is becoming a major public health concern worldwide. Si-Ni-San (SNS) is a famous formula in Traditional Chinese Medicine (TCM) with potent antidepressant effects. However, the antidepressant mechanism of SNS has not been clearly elucidated. This study was performed to verify whether the antidepressant effects of SNS were related to its anti-inflammatory effects, the levels of brain-derived neurotrophic factor (BDNF) and Cytochrome P450 (CYP450) enzymatic activity. In our study, behavioral tests such as the forced swim test, sucrose preference test and open-field test were evaluated to ensure the establishment of depressive rats. The levels of IL-1β, IL-6, and TNF-α in the serum, liver, and hippocampus of rats were measured by enzyme-linked immunosorbent assays (ELISA). Furthermore, the key proteins NF-κB, BDNF, and TrkB were analyzed by Western blot (WB) analysis in the hippocampus. In addition, CYP450 enzymatic activity analysis was performed using LC-MS/MS in conjunction with drug and statistics (DAS 3.0) after oral administration of six probe drugs. Our results showed that SNS attenuated reserpine-induced increases in IL-1β, IL-6, and TNF-α expression in the serum, liver, and hippocampus. The levels of NF-κB, BDNF, and TrkB in the hippocampus of depressive rats were also altered. According to the pharmacokinetic parameters, SNS had moderate inhibitory effects in the reserpine-induced depression model on CYP1A2, CYP2D1, CYP2E1, and CYP3A2, but no significant metabolic changes to CYP2C6 and CYP2D2. These findings suggested that SNS has a protective effect on reserpine-induced depressive rats, which may be related to the improvement of the inflammatory factors, the level of BDNF and the activity of CYP450 enzymes.

Blockade of the dopaminergic neurotransmission with AMPT and reserpine induces a differential expression of genes of the dopaminergic phenotype in substantia nigra

Dopaminergic neurons have the ability to release Dopamine from their axons as well as from their soma and dendrites. This somatodendritically-released Dopamine induces an autoinhibition of Dopaminergic neurons mediated by D2 autoreceptors, and the stimulation of neighbor GABAergic neurons mediated by D1 receptors (D1r). Here, our results suggest that the somatodendritic release of Dopamine in the substantia nigra (SN) may stimulate GABAergic neurons that project their axons into the hippocampus. Using semiquantitative multiplex RT-PCR we show that chronic blockade of the Dopaminergic neurotransmission with both AMPT and reserpine specifically decreases the expression levels of D1r, remarkably this may be the result of an antagonistic effect between AMPT and reserpine, as they induced the expression of a different set of genes when treated by separate. Furthermore, using anterograde and retrograde tracing techniques, we found that the GABAergic neurons that express D1r also project their axons in to the CA1 region of the hippocampus. Finally, we also found that the same treatment that decreases the expression levels of D1r in SN, also induces an impairment in the performance in an appetitive learning task that requires the coding of reward as well as navigational skills. Overall, our findings show the presence of a GABAergic interconnection between the SNr and the hippocampus mediated by D1r.

Intracerebroventricular injection of deltamethrin increases locomotion activity and causes spatial working memory and dopaminergic pathway impairment in rats

Deltamethrin (DM) is widely used in agriculture, veterinary medicine and control of domestic pests. Epidemiological studies suggest that DM exposure is a risk factor for neurodegenerative disorders such as Parkinson's (PD) and Alzheimer diseases; however the mechanisms are elusive. In the present study we evaluated the effects of intracerebroventricular (i.c.v.) administration of DM on locomotion activity, spatial working memory and dopaminergic pathway in the rat. Middle-aged male Wistar rats received three i.c.v. injections of DM 0.5 μg, DM 5 μg or vehicle, every other day. Across the treatment, the animals were submitted to behavioral evaluation in the catalepsy test, open field test, and spontaneous alternation task. Following completion of behavioral tests, rats were perfused and their brains were processed to tyrosine hydroxylase (TH) immunohistochemistry. We observed that i.c.v. administration of DM 5 μg increased locomotion activity (open field) and caused spatial working memory impairment (spontaneous alternation task). These alterations were accompanied by reduction TH immunoreactivity in the substantia nigra pars compacta (SNpc), ventral tegmental area (VTA) and dorsal striatum. Conversely, no motor change was observed in the catalepsy test. These results indicate that i.c.v. administration of DM can cause hyperactivity and cognitive alteration which may be related to disruption of the dopaminergic pathway.

Eplingiella fruticosa leaf essential oil complexed with β-cyclodextrin produces a superior neuroprotective and behavioral profile in a mice model of Parkinson's disease

Evidence indicates that oxidative stress has an important role in the onset and progression of Parkinson's disease (PD). Antioxidant agents from natural products have shown neuroprotective effects in animal models of PD. Eplingiella fruticosa is an aromatic and medicinal plant of the Lamiaceae family that include culinary herbs. The essential oil (EPL) has anti-inflammatory and antioxidant activities. Cyclodextrins are used to enhances pharmacological profile of essential oil. We obtained the EPL from leaves and complexed with β-cyclodextrin (EPL-βCD). Phytochemical analysis showed as main constituents: β-caryophyllene, bicyclogermacrene and 1,8-cineole. We evaluated the effects of EPL and EPL-βCD (5 mg/kg, p.o. for 40 days) on male mice submitted to the progressive reserpine PD model. Behavioral evaluations, lipid peroxidation quantification and immunohistochemistry for tyrosine hydroxylase were conducted. EPL delayed the onset of catalepsy and decreased membrane lipid peroxides levels in the striatum. EPL-βCD also delayed the onset of catalepsy, reduced the frequency of oral diskynesia, restored memory deficit, produced anxiolytic activity and protected against dopaminergic depletion in the striatum and SNpc. These findings showed that EPL has a potential neuroprotective effect in a progressive PD animal model. Further, EPL-βCD enhanced this protective effects, suggesting a novel therapeutic approach to ameliorate the symptoms of PD.

Animal models of early-stage Parkinson's disease and acute dopamine deficiency to study compensatory neurodegenerative mechanisms

Parkinson's disease is a common neurodegenerative disease characterized by a widely variety of motor and non-motor symptoms. While the motor deficits are only visible following a severe dopamine depletion, neurodegenerative process and some non-motor symptoms are manifested years before the motor deficits. Importantly, chronic degeneration of dopaminergic neurons leads to the development of compensatory mechanisms that play roles in the progression of the disease and the response to anti-parkinsonian therapies. The identification of these mechanisms will be of great importance for improving our understanding of factors with important contributions to the disease course and the underlying adaptive process. To date, most of the data obtained from animal models reflect the late, chronic, dopamine-depleted states, when compensatory mechanisms have already been established. Thus, adequate animal models with which researchers are able to dissect early- and late-phase mechanisms are necessary. Here, we reviewed the literature related to animal models of early-stage PD and pharmacological treatments capable of inducing acute dopamine impairments and/or depletion, such as reserpine, haloperidol and tetrodotoxin. We highlighted the advantages, limitations and the future prospective uses of these models, as well as their applications in the identification of novel agents for treating this neurological disorder.